An oxygen sensor is a device configured to measure oxygen partial pressure using a sensor used for a double oxygen sensor system and feedback the measured oxygen partial pressure to an engine control unit (ECU). Through this, a three way catalyst configured to eliminate nitrogen oxide (NOx), hydrocarbon (HC), and carbon monoxide (CO) included in an exhaust gas is used under an optimum condition.
A binary-type oxygen sensor which is being applied to most current vehicles uses oxygen included in the atmosphere being suctioned into a sensing unit through an inlet hole, which leads from a central portion of the oxygen sensor to the atmosphere, as reference oxygen to detect an oxygen concentration included in an exhaust gas.
In addition, when there is no atmosphere inlet hole, oxygen used for detecting an oxygen concentration in an exhaust gas is used by directly charging the exhaust gas into a reference electrode of an oxygen sensor element, and the oxygen is used as reference oxygen.
In this case, a planar-type oxygen sensor of the binary-type oxygen sensor uses zirconia, which is a typical oxygen ion conductor, as a medium for detecting an amount of exhausted oxygen.
In such a planar-type oxygen sensor, a sensing electrode is disposed on a detecting surface to be exposed to an exhaust gas, a reference electrode is disposed in a solid electrolyte layer to be located in a portion under the sensing electrode, and a heating unit configured to heat the solid electrolyte layer is disposed in a portion under the reference electrode.
Because of this, since the solid electrolyte layer is sequentially and upwardly heated by the heating unit, there is a problem in that a total response speed is slow.
In addition, since a heating unit made of a different material from the other components is biased toward and disposed at a lower side in an entire structure thereof, differences in expansion and contraction rates occur due to a difference in a material thereof when expansion occurs by sintering or heating, and thus there is a problem in that cracking or bending occurs.
Meanwhile, an electrical connection structure among a heating unit, a reference electrode, and a terminal is configured such that a via hole of the heating unit is formed vertically downward and a via hole of the reference electrode is formed vertically upward so as to be connected to the terminal.
However, when a heating unit is disposed between a reference electrode and a sensing electrode and via holes are formed in a conventional manner, there is a structural problem in that the via holes configured to connect the reference electrode and a terminal have to be pass through the heating unit to be installed.
Accordingly, a new method for solving these problems is required.